I don't know if I can pick a single favorite. I love muskie fishing, bass, trout, steelhead, catfish... Around here we have some pretty big flathead catfish and I like to night fish for those in the summer with live bluegills for bait. I only did that once this year and didn't catch anything big. Well, a 15 pound snapping turtle, but no big fish. In past years I've caught 3 over 40 pounds, the biggest taking the scale to it's 50 pound maximum and then breaking it.
If I could fish for anything, I'd go fishing for white sturgeon again. I've only done it once for half a day and was very fortunate to get into a couple of really big fish. The first was about 9 feet long and the second was estimated at 12+, possibly as much as 14. It's hard to get a good measurement when you can't lift the fish out of the water or beach it, but calling it "huge" wouldn't do that fish justice. To say I caught it is a little iffy, too. It might be more accurate to say I hooked it, put everything I had into trying to move it, and it decided to humor me and let me bring it up to the boat. We took pictures and then it stopped finning, lay still and just let its weight take it straight down, and the 80 pound line just popped.